How to make a method to return random string in the format A1A 1A1?

private static readonly Random rng = new Random();

private static RandomChar(string domain)
{
    int selection = rng.Next(domain.Length);
    return domain[selection];
}

private static char RandomDigit()
{
    return RandomChar("0123456789");
}

private static char RandomLetter()
{
    return RandomChar("ABCDEFGHIJKLMNOPQRSTUVWXYZ");
}

public static char RandomStringInSpecialFormat()
{
    char[] text = new char[6];
    char[0] = RandomLetter();
    char[1] = RandomDigit();
    char[2] = RandomLetter();
    char[3] = RandomDigit();
    char[4] = RandomLetter();
    char[5] = RandomDigit();
    return new string(text);
}

private int RandomNumber(int min, int max)
{
    Random random = new Random();
    return random.Next(min, max);
}

public static string RandomString(Random rand, int length)
    {
        char[] str = new char[length];
        for (int i = 0; i < length; i++)
        {
            if (i % 2 == 0)
            {    //letters
                str[i] = (char)rand.Next(65, 90);
            }
            else
            {
                //numbers
                str[i] = (char)rand.Next(48, 57);
            }
        }
        return new string(str);
    }

if (i % 2 == 0)
{
      //letters
      str[i] = (char)rand.Next('A', 'Z');
}
else
{
   //numbers
    str[i] = (char)rand.Next('0', '9');
}

class Program
{
    static void Main(string[] args)
    {
        Random r = new Random();
        for(int i = 0;i<25;i++)
        Console.WriteLine(RandomString(r,6));
        Console.Read();
    }

    public static string RandomString(Random rand, int length)
    {
        char[] str = new char[length];
        for (int i = 0; i < length; i++)
            str[i] = (char)rand.Next(65 - (17 * (i % 2)), 91-(33 * (i % 2)));
        return new string(str);
    }
}